An oven of this type is disclosed in EP-A 558 151. The conveyor belt thereof is held clamped around the two drums under the influence of a pretensioning force. The drums can drive the conveyor belt under the influence of the friction generated by this pretensioning force.
The conveyor belt is additionally subjected to the tensile force generated by the drums, which is required in order to propel the conveyor belt in the direction of transport. This tensile force can be appreciable since it must be greater than the frictional forces produced by the means supporting the transport.
The support for the conveyor belt comprises a number, usually two or three, of parallel guide sections over which the conveyor belt slides. At the location of the drums said frictional forces are directly cancelled out by the driving action of the drums, so that the tensile forces in the conveyor belt remain restricted at this location. However, especially in the belt return loop and in the section of the conveyor belt that crosses between the drums fairly high tensile forces arise.
The tensile forces arising in the belt return loop are partly compensated for by an axillary drive unit which is connected to a return shaft at the location of the entrance to the housing.
These problems, which are associated with the tensile force in the conveyor belt, arise to an increased extent in ovens of a larger capacity, that is to say ovens with a fairly broad conveyor belt. In particular the section of the conveyor belt that forms the crossover from the first to the second helical path is exposed to fairly high tensile forces.